Al, Cr, Ni—Al, Pt—Al, MCrAlY are well-known examples of oxidation-resistant, anticorrosion coating materials commonly used for the turbine rotor blades and turbine stator vanes of many jet engines and industrial gas turbines. When these coating materials are used for the turbine blades made of a Ni-base superalloy, interdiffusion of elements proceeds at the interface between the Ni-base superalloy and the coating material upon extended use of the turbine blades at high temperatures. The element interdiffusion degrades the material of the Ni-base superalloy, which causes various technical problems such as degradation of strength and degradation of the environment resistance of the coating material. These can be detrimental to the durability of the turbine blade itself. Such a diffusion phenomenon is accelerated at the high gas temperatures of the recent jet engines and gas turbines, because the increased gas temperature inevitably raises the temperature of the turbine blades. The adverse effect of the diffusion region becomes even more problematic with the reducing thickness of high-pressure turbine blades, which have a hollow construction for cooling.
A diffusion barrier coating has been proposed that suppresses element diffusion at the substrate/coating interface (see, for example, Patent Document 1). The limitation of the diffusion barrier coating, however, is that it is a multilayer structure and therefore complicates the coating process, and that the substrate and the coating material are not in a state of thermodynamic equilibrium.
The recently published U.S. Patent Application 2004/0229075 (Patent Document 2) discloses limiting Al diffusion using a γ+γ′ phase coating that contains a Pt-group metal with a reduced concentration of Al, which is the fastest diffusing element and generates a deleterious phase by diffusion. However, as above, the effect is still limited because the substrate and the coating material are not in a state of thermodynamic equilibrium. As such, during extended use at high temperature, Pt and Al in the coating material diffuse inward while the enhancing element diffuses out of the coating material. As a result, the article deteriorates.
Patent Document 1: U.S. Pat. No. 6,830,827
Patent Document 2: U.S. Patent Application 2004/0229075